The subject matter disclosed herein relates to electromechanical actuators. More specifically, the present disclosure relates to position sensing of electromechanical actuators.
Many systems require actuators to manipulate various components. Rotary actuators rotate an element about an axis, such as flight control surfaces, for example, flaps and ailerons. In such flight applications, there has been a trend toward wings of thinner cross-sections, such that size and space available for placement of the actuator inside of the wing is limited. The trend has led to the use of a rotary actuator of a “hinge-line” design, wherein a rotational axis of the actuator is aligned with that of the flight control surface and the actuator acts as a hinge (hence the term “hinge-line”). This trend also raises the need for such an actuator with a tighter cross-section to fit the available space.
Such actuators often use position sensing apparatus to sense and track the actuator position. As the sizes of the actuators are reduced in response to the thin wing trend, the volume occupied by a conventional position sensor becomes a significant percentage of the total actuator volume and a significant percentage of the cost. Typical position sensing for electromechanical actuators tends to fall into two categories, rotary variable differential transformer (RVDT) and encoders. Whereas RVDTs provide absolute position determination on startup, they are relatively large and expensive. Encoders, while smaller and less expensive than RVDTs, require some motion at startup to determine the position.